System for regulating the dispensing of commercial aircraft passenger oxygen supply

ABSTRACT

The aircraft emergency oxygen supply system includes one or more sources of supplemental breathable oxygen, one or more inlet valves for one or more breathing devices, connected to the inlet valves, and one or more cabin air pressure transducers. A pressure controller controls the inlet valves in response to the one or more cabin air pressure transducers. One or more second pressure transducers may connected to conduits downstream of inlet valves to be monitored, and the pressure controller may also control operation of the inlet valves in response to the one or more second pressure transducers.

BACKGROUND OF THE INVENTION

This invention relates to the metering and control of fluids, and moreparticularly relates to the metering and control of fluids of aircraftpassenger supplemental oxygen, particularly as would be used in acommercial aircraft airliner.

Emergency oxygen supply systems, such as are typically installed onaircraft to supply oxygen to passengers upon loss of cabin pressure ataltitudes above about 12,000 feet, typically include a source ofsupplemental breathable oxygen connected to a face mask that is releasedfrom an overhead storage compartment when needed. The flow of breathableoxygen should be sufficient to sustain passengers until cabin pressureis re-established, or until a lower, safer altitude can be reached.

Presently, in passenger oxygen systems of large aircraft utilizing agaseous oxygen supply source, oxygen is typically distributed from acentrally located bank of storage vessels or cylinders by a network ofpiping to manifolds that are commonly located adjacent to each row ofseats. Each passenger mask is typically supplied via a separate orificeof the manifold. By varying the input pressure to the manifolds, theflow of oxygen to each of the masks can be varied.

When the emergency oxygen is to be supplied to a face mask, a constantflow of oxygen is typically received by a reservoir bag attached to theface mask. The oxygen is commonly supplied continuously at a rate thatis calculated to accommodate even the needs of a passenger with asignificantly larger than average tidal volume who is breathing at afaster than average respiration rate. The continuing flow of oxygen intothe reservoir bag and into the mask is typically diluted by cabin air.

Inefficiencies in aircraft emergency oxygen supply systems can requirethe emergency oxygen supply to be larger and heavier than necessary,which has an adverse impact on the payload capacity and fuel consumptionof the aircraft. For example, one known aircraft emergency oxygen supplysystem delivers a fixed oxygen flow suitable for the maximum cabinaltitude contemplated, regardless of the actual cabin altitude thatprevails. While this is a safe approach, it results in high oxygenconsumption that requires a large and heavy oxygen supply.

Enhancing the efficiency of such aircraft emergency oxygen supplysystems either in terms of the generation, storage, distribution orconsumption of oxygen could therefore yield a weight savings.Conversely, an enhancement of an aircraft emergency oxygen supplysystem's efficiency without a commensurate downsizing would impart alarger margin of safety in the system's operation. It is thereforehighly desirable to enhance the efficiency of an emergency oxygen supplysystem in any way possible.

The delivered supplemental oxygen flow rate needed to properly oxygenatean aircraft cabin occupant depends on the prevailing pressure altitude.The quantity of oxygen delivered to a user can advantageously be variedas a function of altitude, so that the quantity delivered producesproper oxygenation, while avoiding an inefficient and wasteful deliveryof a greater quantity of oxygen than is required.

While efficient delivery of oxygen to each cabin occupant at the minimumrequired flow rate for a given altitude is desirable, variations inoxygen delivery to various masks distributed about the cabin due tovariations in the pressure drop between locations in the piping systemcan result in some oxygen masks receiving oxygen flow at a lower ratethan the average rate of oxygen flow. Because the system design isrequired to ensure that even the least favored mask must receive asufficient supply, it follows that more oxygen than the minimum amountrequired to suitably oxygenate the user of a mask can be delivered to amask receiving an average oxygen flow. Delivery of an average excessoxygen to masks to compensate for pressure variations within thedistribution system constitutes a second inefficiency in the delivery ofoxygen.

One conventional response to the issue of altitude variations has beenthe use of a so-called “altitude compensating regulator.” In a typicalaltitude compensating regulator, an aneroid barometer adjusts the outputpressure of the regulator in response to changes in pressure altitudewithin the cabin. However, altitude compensating regulators oftendeliver an optimum flow at one altitude range and greater-than-optimumflow at other altitudes, as a consequence of the operating principlesand control laws that govern the performance of pneumatic oxygenregulators. Further, a centrally located altitude compensating regulatorfails to address the differences in flow rates at various locations inthe piping network that result from variations in pressure drops withindifferent regions of the piping network.

A disadvantage of a conventional electronic altitude compensatingregulator is that the controller must be capable of generating signalsthat can move the valve to a multiplicity of positions, adding tocomplexity and cost. The valve also must have features that render itcapable of responding by adopting a multiplicity of positions.Furthermore, the use of a single electronic regulator does not addressthe issue of different flows being delivered at different locations inthe aircraft due to the varied pressure drops in the distribution lines.

One conventional aircraft emergency oxygen supply system utilizes anelectrically operated valve that is capable of assuming a multiplicityof states between fully open and fully closed. This approach allows theaircraft emergency oxygen supply system to operate more efficiently at arange of altitudes, but utilizes a valve that is complex in itsprinciple of operation and its performance, and that is thereforeexpensive and difficult to design and manufacture.

Another conventional aircraft emergency oxygen supply system suppliespassengers with a first fraction of air enriched in oxygen from highpressure oxygen cylinders during a descent phase of the aircraft betweena normal cruising altitude and an intermediate rerouting altitude.Compressed air is taken from a source of compressed air in the aircraftto produce a second fraction of air enriched in oxygen delivered topassengers during a phase of stabilized flight of the aircraft greaterthan 5,500 meters.

Another conventional aircraft emergency oxygen supply system calculatesoxygen required and monitors the oxygen supply and flight level afteremergency cabin decompression. The system utilizes a pressurized oxygensupply which feeds oxygen into the interior of the plane when it fliesat high cabin altitudes, and the system indicates the changing status ofthe supply as oxygen is drained from the system. The system includes apressure transducer coupled to the supply, and determines the rate atwhich the pressure of the supply is reduced, to yield a first signalrepresenting this pressure lapse rate, and to concurrently determine thelapse rate at which the number of liters of oxygen in the supply isreduced, to yield a second signal representing the liter lapse rate.When oxygen is being drained from the supply, the system calculates theprevailing supply pressure, the number of liters remaining in thesupply, and the time in hours and minutes remaining before the supply isexhausted, based on the current rate of oxygen consumption.

Another known aircraft emergency oxygen supply system includespressurized oxygen storage for feeding a pipe with pressurized oxygen,and a distribution unit that responds to loss of pressurization at highaltitude. The distribution unit delivers pressurized oxygen at apressure that increases up to a first value that is reached when loss ofpressurization occurs under an altitude of about 40,000 feet, anddelivers pressurized oxygen at a pressure at a second value of about twotimes the first value, at an altitude above about 40,000 feet.

It would be desirable to provide an aircraft emergency oxygen supplysystem utilizing a simple electrically operated valve having on and offpositions in combination with one or more suitable pressure transducersand suitable control logic to supply oxygen in a manner that is adjustedin response to the prevailing cabin altitude, to ensure that sufficientsupplemental oxygen is dispensed for the particular cabin altitudecondition that prevails, without dispensing more oxygen than is neededunder the altitude condition, and to minimize the weight of theassociated oxygen supply. It would also be desirable to provide anaircraft emergency oxygen supply system that efficiently uses multiplecontrol zones within an aircraft, as well as multiple oxygen storagesources that are distributed through the aircraft. The present inventionsatisfies these and other needs.

SUMMARY OF THE INVENTION

Briefly, and in general terms, the invention provides for an aircraftemergency oxygen supply system utilizing an electrically operated on-offinlet valve in combination with one or more suitable pressuretransducers and one or more suitable controllers to supply supplementaloxygen as needed at a prevailing cabin altitude, without dispensing moreoxygen than is needed, minimizing the weight of the oxygen supply, andallowing efficient use of multiple control zones and oxygen sourceswithin an aircraft.

Accordingly, the present invention provides for an aircraft emergencyoxygen supply system including one or more sources of supplementalbreathable oxygen, each connected to a corresponding inlet valve. In oneaspect, the inlet valves are on-off inlet valves, such as two-positionsolenoid valves. One or more breathing devices are connected to eachinlet valve, and one or more cabin air pressure transducers are providedfor generating a cabin air pressure input signal representing the cabinpressure and a corresponding altitude. A pressure controller isconnected to the inlet valves and is configured to control the operationof the inlet valves in response to the input signals received from theone or more cabin air pressure transducers. This arrangement allows fora zoned-system architecture, with one or more pressure controllers andtheir corresponding sources of supplemental breathable oxygen, inletvalves, breathing devices and cabin air pressure transducers placed invarious locations within the aircraft. In another aspect, the inletvalves may include an upstream first inlet valve, and a downstreamsecond inlet valve connected downstream to the first inlet valve, andthe one or more breathing devices are connected to the downstream secondinlet valve.

In another aspect, the invention provides for an aircraft emergencyoxygen supply system that includes a plurality of sources ofsupplemental breathable oxygen, a corresponding plurality of inletvalves connected to the plurality of sources of supplemental breathableoxygen, respectively, a corresponding plurality of breathing devicesconnected to the plurality of inlet valves, respectively, and one ormore pressure controllers connected to the plurality of inlet valves andconfigured to control the operation of the plurality of inlet valves. Aplurality of conduits may be connected between the plurality of sourcesof supplemental breathable oxygen and the corresponding plurality ofinlet valves, respectively, to provide a flow of oxygen to the pluralityof inlet valves. In another presently preferred aspect, the inlet valvesmay include a corresponding plurality of upstream first on-off inletvalves, respectively, and a corresponding plurality of downstream secondon-off inlet valves, respectively, connected downstream serially to theplurality of first on-off inlet valves, respectively, and the pluralityof breathing devices are connected to the corresponding plurality ofdownstream second on-off inlet valves, respectively.

In one presently preferred aspect, the one or more cabin air pressuretransducers may be configured to generate a cabin air pressure inputsignal representing a cabin pressure and a corresponding altitude. Inanother presently preferred aspect, one or more second pressuretransducers also may be connected to one of the conduits at a locationdownstream of one of the inlet valves to be monitored, to generate a gaspressure input signal representing a gas pressure downstream of themonitored valve. The one or more pressure controllers control theoperation of the inlet valves in response to the first input signalreceived from the first pressure transducer representing the cabinpressure and a corresponding altitude, and in response to the secondinput signal received from the second pressure transducer. The one ormore second pressure transducers may include a plurality of secondpressure transducers connected to the conduits downstream from theupstream first on-off inlet valves, respectively, and a plurality ofthird pressure transducers connected to the conduits downstream from thedownstream second on-off valves, respectively, representing a gaspressure downstream of the monitored valves, in which case the one ormore pressure controllers control the operation of the inlet valves inresponse to the first input signal received from the first pressuretransducer representing the cabin pressure and a corresponding altitude,and in response to the plurality of second pressure transducers and theplurality of third pressure transducers. The one or more pressurecontrollers compare a measured pressure downstream with a desireddelivery pressure, and if the measured downstream pressure is greaterthan or equal to the desired delivery pressure, the one or more pressurecontrollers are operative to close the inlet valves, and if the measureddownstream pressure is lower than the desired delivery pressure, the oneor more pressure controllers are operative to momentarily open the inletvalves.

In another presently preferred aspect, the emergency oxygen supplysystem further includes one or more manifolds connected between one ormore inlet valves and one or more breathing devices, respectively. Inanother presently preferred aspect, the emergency oxygen supply systemmay further include a corresponding plurality of pressure reducingregulators connected to the plurality of sources of supplementalbreathable oxygen, respectively. In another aspect, the plurality ofpressure reducing regulators include no altitude-compensating features.

Other features and advantages of the present invention will become moreapparent from the following detailed description of the preferredembodiments in conjunction with the accompanying drawings, whichillustrate, by way of example, the operation of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a first embodiment of the system forregulating the dispensing of commercial aircraft passenger oxygensupply, according to the present invention.

FIG. 2 is a schematic diagram of a second embodiment of the system forregulating the dispensing of commercial aircraft passenger oxygensupply, according to the present invention.

FIG. 3 is a schematic diagram of a third embodiment of the system forregulating the dispensing of commercial aircraft passenger oxygensupply, according to the present invention.

FIG. 4 is a schematic diagram of a fourth embodiment of the system forregulating the dispensing of commercial aircraft passenger oxygensupply, according to the present invention.

FIG. 5 is a schematic diagram of a variation of the fourth embodiment ofFIG. 4.

FIG. 6 is a schematic diagram of a fifth embodiment of the system forregulating the dispensing of commercial aircraft passenger oxygensupply, according to the present invention.

FIG. 7 is a schematic diagram of a variation of the fifth embodiment ofFIG. 6.

FIG. 8 is a schematic diagram of a sixth embodiment of the system forregulating the dispensing of commercial aircraft passenger oxygensupply, according to the present invention.

FIG. 9 is a schematic diagram of a seventh embodiment of the system forregulating the dispensing of commercial aircraft passenger oxygensupply, according to the present invention.

FIG. 10 is a schematic diagram of a eighth embodiment of the system forregulating the dispensing of commercial aircraft passenger oxygensupply, according to the present invention.

FIG. 11 is a schematic diagram of a ninth embodiment of the system forregulating the dispensing of commercial aircraft passenger oxygensupply, according to the present invention.

FIG. 12 is a schematic diagram of a variation of the ninth embodiment ofFIG. 11.

FIG. 13 is a schematic diagram of a tenth embodiment of the system forregulating the dispensing of commercial aircraft passenger oxygensupply, according to the present invention.

FIG. 14 is a schematic diagram of a variation of the tenth embodiment ofFIG. 13.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the drawings, which are provided for purposes ofillustration and by way of example, the present invention provides foran aircraft emergency oxygen supply system utilizing an electricallyoperated on-off inlet valve in combination with one or more suitablepressure transducers and one or more pressure controllers to supplysupplemental oxygen appropriate for the prevailing cabin altitude,without dispensing more oxygen than is needed, minimizing the weight ofthe oxygen supply, and allowing efficient use of multiple control zonesand oxygen sources within an aircraft.

In a first preferred embodiment of the emergency oxygen supply system 10of the present invention, illustrated in FIG. 1, a plurality of sourcesof supplemental breathable oxygen 12 a, 12 b, 12 c, such as a pluralityof cylinders of compressed oxygen, for example, store a required supplyof oxygen. Corresponding conduits 14 a, 14 b, 14 c are connected to theplurality of sources of supplemental breathable oxygen, respectively, toprovide a flow of oxygen, controlled by corresponding relatively simpleon-off inlet valves 16 a, 16 b, 16 c, respectively, to correspondingsets of breathing devices 18 a, 18 b, 18 c typically including one ormore individual reservoir bags and attached face masks, respectively. Inone presently preferred aspect, the inlet valves are located inproximity to the corresponding plurality of sources of supplementalbreathable oxygen. At least one pressure controller 20 is connected tothe inlet valves and controls the operation of the inlet valves via anetwork of control lines 22, in response to an input signal receivedfrom a single cabin air pressure transducer P_(A) (24) representing thecabin pressure and a corresponding altitude. This configuration resultsin a system that is lighter than one without altitude compensation, andsimpler than one that uses conventional altitude compensation with amultiplicity of complex regulators.

In a second embodiment of the invention illustrated in FIG. 2, anemergency oxygen supply system 30 includes a plurality of sources ofsupplemental breathable oxygen 32 a, 32 b, 32 c, such as a plurality ofcylinders of compressed oxygen, for example, that store a requiredsupply of oxygen. Corresponding conduits 34 a, 34 b, 34 c are connectedto the plurality of sources of supplemental breathable oxygen,respectively, to provide a flow of oxygen, controlled by correspondingrelatively simple on-off inlet valves 36 a, 36 b, 36 c, respectively,such as two-position solenoid valves, for example, to corresponding setsof breathing devices 38 a, 38 b, 38 c, typically including one or moreindividual reservoir bags and attached face masks, respectively. In onepresently preferred aspect, the inlet valves are located in proximity tothe corresponding plurality of sources of supplemental breathableoxygen. At least one pressure controller, such as the pressurecontroller 40, is connected to the inlet valves and controls theoperation of the inlet valves via a network of control lines 42 inresponse to a first input signal received from a first pressuretransducer P_(A) (44) representing the cabin pressure and acorresponding altitude, and in response to a second input signalreceived from a second pressure transducer P_(D) (46) connected to oneof the conduits at a location 48 downstream of one of the inlet valvesto be monitored, representing the current gas pressure downstream of themonitored valve. From the input from the downstream pressure transducerP_(D), the controller compares a current gas pressure downstream (P_(D))with a desired delivery pressure. If the current downstream pressure isgreater than or equal to the desired delivery pressure, the inlet valvesremain closed. If the downstream pressure is lower than desired, thecontroller momentarily opens the valves, releasing added oxygen into thedownstream portion of the oxygen distribution system and raising thedownstream pressure.

Within this embodiment, the valves could be opened for an interval thatis constant for each opening event, and the delivery would then becontrolled solely by adjusting the duration of the time between pulses.Alternatively, both the length of the opening interval and the durationof the closed time between intervals could be each adjusted to achievethe overall result.

Since oxygen flows out of the system through the breathing devices, thepressure at the point where the downstream pressure is measured wouldvary somewhat as a function of time, dropping continuously when thevalves are closed and increasing continuously when the valves areopened. The magnitude of the contained volume of the system downstream,relative to the volume rate of flow out of the system, would affect themagnitude of such variations. By suitably varying the time scale of theon and off intervals, the output pressure can be adjusted to suitablyapproximate a steady state.

Many oxygen systems for aircraft passengers utilize as the oxygendispensing device the type of constant flow oxygen mask that is known asa “phase dilution mask.” Such masks are contemplated by SAE AerospaceStandard AS8025. The mask has a reservoir that collects oxygen deliveredduring the portions of the breathing cycle when the user is exhaling andduring the pause between breaths, and this collected oxygen is thendelivered at the beginning of the next inhalation. If the time scale ofthe variation in delivery pressure is short relative to the time scaleof the breathing cycle, the output pressure would be considered to beapproximating a steady state in a manner suitable for the purpose ofsupplying such a mask.

Thus, in the second embodiment of the invention, a simple inlet valvesuch as a two position solenoid valve can replace a more complicated andcostly control valve. In association with this change in valve type, thecontroller is also correspondingly simpler because it is only requiredto generate a simple “on” or “off” signal.

In a third embodiment of the invention illustrated in FIG. 3, multiplesimple inlet valves are placed at various locations within the oxygendistribution piping system, with a pressure transducer downstream ofeach valve. In this embodiment, the emergency oxygen supply system 50includes a plurality of sources of supplemental breathable oxygen 52 a,52 b, 52 c, such as a plurality of cylinders of compressed oxygen, forexample, that store a required supply of oxygen. Corresponding conduits54 a, 54 b, 54 c are connected to the plurality of sources ofsupplemental breathable oxygen, respectively, to provide a flow ofoxygen, controlled by corresponding first relatively simple upstreamon-off inlet valves V₁ (56 a), V₃ (56 b), V₅ (56 c), respectively, andcorresponding second relatively simple downstream on-off inlet valves V₂(58 a), V₄ (58 b), V₆ (58 c), respectively, such as two-positionsolenoid valves, for example, connected serially to corresponding setsof breathing devices 60 a, 60 b, 60 c, each typically including one ormore individual reservoir bags and attached face masks, respectively. Atleast one pressure controller, such as a single pressure controller 62,is connected to the inlet valves and controls the operation of the inletvalves via a network of control lines 63 in response to input signalsreceived from a first pressure transducer P_(A) (64), representing thecabin pressure and a corresponding altitude, and input signals receivedfrom a plurality of second pressure transducers P₁ (66 a), P₃ (66 b), P₅(66 c), downstream from the upstream on-off valves V₁, V₃, V₅,respectively, and input signals received from a plurality of secondpressure transducers P₂ (68 a), P₄ (68 b), P₆ (68 c), downstream fromthe downstream on-off valves V₂, V₄, V₆, respectively, representing thecurrent gas pressure downstream of the monitored valves. Each valve andassociated pressure transducer set is connected to the controller by aseparate set of wires. The controller may have multiple independentchannels, so that each valve and associated pressure transducer has adedicated control channel. Alternatively, the pressure controller couldbe sequenced so that the signal from one downstream pressure transducerat a time is read, and its associated valve is pulsed if the pressurevalue detected is low enough to require this action.

In this embodiment, oxygen delivery pressure can be set to an optimumvalue zone by zone, without performance being limited by the differencesin flow rates at various locations in the piping network that resultfrom variations in pressure drops within different regions of the pipingnetwork.

In a fourth embodiment of the invention, illustrated in FIG. 4, anemergency oxygen supply system 70 includes a plurality of sources ofsupplemental breathable oxygen 72 a, 72 b, 72 c, such as a very largenumber of separate, relatively small oxygen cylinders that aredistributed throughout the airplane. In the limiting case of such anapproach, each cabin occupant may be served by a separate one-personcylinder. Corresponding conduits 74 a, 74 b, 74 c are connected to theplurality of sources of supplemental breathable oxygen, respectively, toprovide a flow of oxygen, controlled by corresponding relatively simpleon-off inlet valves 76 a, 76 b, 76 c, respectively, such as two-positionsolenoid valves, for example, to corresponding individual breathingdevices 78 a, 78 b, 78 c typically including one or more individualreservoir bags and attached face masks, respectively. Since the pipingbetween the small cylinders and the few breathing devices supplied withoxygen would be relatively simple, the pressure drops would all beessentially equal, so there would be little or no need to deliver excessoxygen to the average breathing device in a given zone in order toensure the least favored breathing device in the zone is notunder-supplied. Each oxygen vessel is fitted with a simple pressurereducing regulator 80 a, 80 b, 80 c, respectively, with noaltitude-compensating features included. In such an approach to oxygensystem design that uses many small, separate cylinders, the controllershould be very capable, either equipped with a very large number ofsimultaneously operating separate channels or capable of managing a verylarge number of signals in rapid sequence. Downstream of each valve, amanifold 82 a, 82 b, 82 c, fitted with one or more dispensing orifices,is interposed between the corresponding valve and its associatedreservoir bag, respectively. Each manifold orifice supplies onebreathing device. If there are two or more dispensing orifices present,the oxygen manifold is configured such that all of these dispensingorifices experience the same upstream oxygen pressure.

At least one pressure controller, such as a single pressure controller84, is connected to and controls the operation of the inlet valves via anetwork of control lines 86 in response to a first input signal receivedfrom a single pressure transducer P_(A) (88), representing the cabinpressure and a corresponding altitude. The controller evaluates thepressure transducer signal and generates a single signal to all of thesimple inlet valves. In this case, there is an intrinsic flow rate thatwould be achieved through each dispensing orifice if the simple inletvalves were continuously open. This intrinsic flow rate is a function ofthe output pressure from the pressure reducer and the properties of thedispensing orifices. Depending on the flow that is appropriate for thegiven altitude, the valve-operating signal is applied for a suitablefraction of the operating time. The flow rate achieved by eachdispensing orifice is then equal to the intrinsic flow rate possiblemultiplied by the fraction of time the valve is open. For example, ifthe intrinsic flow rate possible when the valve is open continuously is4 liters per minute and the valve is open 30% of the time, the flow rateachieved is 1.2 liters per minute.

As is illustrated in FIG. 5, in a variation of the fourth embodiment, inwhich the same elements from FIG. 4 are indicated by the same referencenumbers as in FIG. 4, more than one cabin occupant may be served by eachoxygen supply cylinder. Corresponding conduits 74 a, 74 b, 74 c areconnected to the plurality of sources of supplemental breathable oxygen,respectively, to provide a flow of oxygen, controlled by correspondingrelatively simple on-off inlet valves 76 a, 76 b, 76 c, respectively,such as two-position solenoid valves, for example, to corresponding setsof a plurality of breathing devices 89 a, 89 b, 89 c, each typicallyincluding one or more individual reservoir bags and attached face masks,respectively. Each oxygen vessel is fitted with a simple pressurereducing regulator 80 a, 80 b, 80 c, respectively, with noaltitude-compensating features included. Downstream of each valve, amanifold 82 a, 82 b, 82 c, fitted with one or more dispensing orifices,is interposed between the corresponding valve and its associatedreservoir bag, respectively. Each manifold orifice supplies more thanone breathing device. At least one pressure controller, such as a singlepressure controller 84, is connected to the inlet valves and controlsthe operation of the inlet valves via a network of control lines 86 inresponse to a first input signal received from a single pressuretransducer P_(A) (88), representing the cabin pressure and acorresponding altitude.

In a fifth embodiment of the invention, illustrated in FIG. 6, anemergency oxygen supply system 90 includes a plurality of sources ofsupplemental breathable oxygen 92 a, 92 b, 92 c, such as a very largenumber of separate, relatively small oxygen cylinders distributedthroughout the airplane. As is shown in FIG. 6, each cabin occupant maybe served by a separate one-person cylinder, although more than oneperson may be served by each oxygen supply cylinder, as is furtherdescribed below. Corresponding conduits 94 a, 94 b, 94 c are connectedto the plurality of sources of supplemental breathable oxygen,respectively, to provide a flow of oxygen, controlled by correspondingrelatively simple on-off inlet valves 96 a, 96 b, 96 c, respectively,such as two-position solenoid valves, for example, to correspondingindividual breathing devices 98 a, 98 b, 98 c typically including one ormore individual reservoir bags and attached face masks, respectively. Inthis embodiment, a pressure reducer at the outlet of the local oxygenvessel is eliminated. Since the piping between the small cylinders andthe few breathing devices supplied with oxygen would be relativelysimple, the pressure drops would all be essentially equal, so therewould be little or no need to deliver excess oxygen to the averagebreathing device in a given zone in order to ensure the least favoredbreathing device in the zone is not under-supplied. Downstream of eachinlet valve, a manifold 99 a, 99 b, 99 c, fitted with one or moredispensing orifices, is interposed between the corresponding inlet valveand its associated reservoir bag, respectively. As is shown in FIG. 6,each manifold orifice supplies one breathing device, although eachmanifold may supply more than one breathing device, as is describedbelow. If there are two or more dispensing orifices present, the oxygenmanifold is configured such that all of these dispensing orificesexperience the same upstream oxygen pressure.

At least one pressure controller, such as a single pressure controller100, is connected to the inlet valves and controls the operation of theinlet valves via a network of control lines 102 in response to a firstinput signal received from a single pressure transducer P_(A) (104),representing the cabin pressure and a corresponding altitude. Thecontroller evaluates the pressure transducer signal and generates asingle signal to all of the simple inlet valves. In this case, there isan intrinsic flow rate that would be achieved through each dispensingorifice if the simple inlet valves were continuously open. Thisintrinsic flow rate is a function of the output pressure from thepressure reducer and the properties of the dispensing orifices.Depending on the flow that is appropriate for the given altitude, thevalve-operating signal is applied for a suitable fraction of theoperating time. The flow rate achieved by each dispensing orifice isthen equal to the intrinsic flow rate possible multiplied by thefraction of time the inlet valve is open. For example, if the intrinsicflow rate possible when the valve is open continuously is 4 liters perminute and the valve is open 30% of the time, the flow rate achieved is1.2 liters per minute.

As is illustrated in FIG. 7, in a variation of the fifth embodiment, inwhich the same elements from FIG. 6 are indicated by the same referencenumbers as in FIG. 6, more than one cabin occupant may be served by eachoxygen supply cylinder. Corresponding conduits 94 a, 94 b, 94 c areconnected to the plurality of sources of supplemental breathable oxygen,respectively, to provide a flow of oxygen, controlled by correspondingrelatively simple on-off inlet valves 96 a, 96 b, 96 c, respectively,such as two-position solenoid valves, for example, to corresponding setsof breathing devices 106 a, 106 b, 106 c, each typically including oneor more individual reservoir bags and attached face masks, respectively.Downstream of each inlet valve, a manifold 99 a, 99 b, 99 c, fitted withone or more dispensing orifices, is interposed between the correspondinginlet valve and its associated reservoir bag, respectively. Eachmanifold orifice supplies more than one breathing device, and eachoxygen manifold is configured such that all of its dispensing orificesexperience the same upstream oxygen pressure. At least one pressurecontroller, such as a single pressure controller 100, is connected tothe inlet valves and controls the operation of the inlet valves via anetwork of control lines 102 in response to a first input signalreceived from a single pressure transducer P_(A) (104) representing thecabin pressure and a corresponding altitude. Interposed between eachoxygen vessel and its associated manifold containing the dispensingorifices, a simple electrical inlet valve is installed. An intrinsicflow rate can be achieved at any given point in time through eachdispensing orifice when the simple inlet valve is open continuously.However, this flow rate changes as the pressure in the oxygen storagevessel upstream of the dispensing orifice decays with the passage oftime during operation of the equipment. The flow rate is a function ofthe operating time history and the pressure decay properties of theoxygen storage units, as well as the properties of the dispensingorifices themselves. In this context, the “operating time” refers to thetime the inlet valve remains open, which is not necessarily equal to thetotal elapsed time since the beginning of a decompression incidentcausing supplemental oxygen to be used.

In the fifth embodiment, a single pressure transducer senses the cabinpressure altitude. The controller contains information thatmathematically describes the way in which the pressure in the oxygenstorage vessel decays as a function of operating time. The controlleralso measures and retains information about the operating time historyduring the period of use. The controller evaluates the pressuretransducer signal and the operating time history and generates a singlesignal to all of the simple inlet valves. Depending on the flow that isappropriate for the combination of given altitude and given previousoperating time history, the valve-operating signal is applied for asuitable fraction of the operating time. The flow rate achieved by eachdispensing orifice is then equal to the intrinsic flow rate possiblemultiplied by the fraction of time the inlet valve is open. While thisembodiment requires greater calculating capabilities in the controller,it eliminates a large number of pressure reducing regulators as well asa large number of pressure transducers and their wiring.

In a sixth preferred embodiment of the emergency oxygen supply system110 of the present invention, illustrated in FIG. 8, a source ofsupplemental breathable oxygen 112, such as one or more cylinders ofcompressed oxygen, for example, serves to store a required supply ofoxygen. A corresponding conduit 114 is connected to the source ofsupplemental breathable oxygen to provide a flow of oxygen, controlledby a relatively simple on-off inlet valve 116, to a set 117 of one ormore breathing devices 118 a, 118 b, 118 c, 118 d, typically includingone or more individual reservoir bags and attached face masks,respectively. In one presently preferred aspect, the inlet valve islocated in proximity to the source of supplemental breathable oxygen. Asingle pressure controller 120 is connected to and controls theoperation of the inlet valve via control line 122 in response to aninput signal received from a single cabin air pressure transducer P_(A)(124), representing the cabin pressure and a corresponding altitude.This configuration results in a system that is lighter than one withoutaltitude compensation, and simpler than one that uses conventionalaltitude compensation with a multiplicity of complex regulators. Thisconfiguration also allows for a zoned-system architecture, with one ormore pressure controllers and their corresponding sources ofsupplemental breathable oxygen, inlet valves, breathing devices andcabin air pressure transducers placed in various locations within theaircraft.

In a seventh embodiment of the invention illustrated in FIG. 9, anemergency oxygen supply system 130 includes a source of supplementalbreathable oxygen 132, such as one or more cylinders of compressedoxygen, for example, to store a required supply of oxygen. A conduit 134is connected to the source of supplemental breathable oxygen to providea flow of oxygen, controlled by a relatively simple on-off inlet valve136, such as a two-position solenoid valve, for example, to acorresponding set 137 of breathing devices 138 a, 138 b, 138 c, 138 d,typically including one or more individual reservoir bags and attachedface masks, respectively. In one presently preferred aspect, the inletvalve is located in proximity to the source of supplemental breathableoxygen. A single pressure controller 140 is connected to and controlsthe operation of the inlet valve via a control line 142 in response to afirst input signal received from a first pressure transducer P_(A)(144), representing the cabin pressure and a corresponding altitude, andin response to a second input signal received from a second pressuretransducer P_(D) (146) connected the conduits at a location 148downstream of the inlet valve to be monitored, representing the currentgas pressure downstream of the monitored inlet valve. From the inputfrom the downstream pressure transducer P_(D), the controller compares acurrent gas pressure downstream (P_(D)) with a desired deliverypressure. If the current downstream pressure is greater than or equal tothe desired delivery pressure, the simple inlet valve remains closed. Ifthe downstream pressure is lower than desired, the controllermomentarily opens the inlet valve, releasing added oxygen into thedownstream portion of the oxygen distribution system and raising thedownstream pressure.

Within this embodiment, the inlet valve could be opened for an intervalthat is constant for each opening event, and the delivery would then becontrolled solely by adjusting the duration of the time between pulses.Alternatively, both the length of the opening interval and the durationof the closed time between intervals could be each adjusted to achievethe overall result. Since oxygen flows out of the system through thebreathing devices, the pressure at the point where the downstreampressure is measured would vary somewhat as a function of time, droppingcontinuously when the inlet valve is closed and increasing continuouslywhen the inlet valve is opened. The magnitude of the contained volume ofthe system downstream, relative to the volume rate of flow out of thesystem, would affect the magnitude of such variations. By suitablyvarying the time scale of the on and off intervals, the output pressurecan be adjusted to suitably approximate a steady state.

Many oxygen systems for aircraft passengers utilize as the oxygendispensing device the type of constant flow oxygen mask that is known asa “phase dilution mask.” Such masks are contemplated by SAE AerospaceStandard AS8025. The mask has a reservoir that collects oxygen deliveredduring the portions of the breathing cycle when the user is exhaling andduring the pause between breaths, and this collected oxygen is thendelivered at the beginning of the next inhalation. If the time scale ofthe variation in delivery pressure is short relative to the time scaleof the breathing cycle, the output pressure would be considered to beapproximating a steady state in a manner suitable for the purpose ofsupplying such a mask.

Thus, in the seventh embodiment of the invention, a simple inlet valvesuch as a two position solenoid valve can replace a more complicated andcostly control valve. In association with this change in valve type, thecontroller is also correspondingly simpler because it is only requiredto generate a simple “on” or “off” signal. This configuration alsoallows for a zoned-system architecture, with one or more pressurecontrollers and their corresponding sources of supplemental breathableoxygen, inlet valves, breathing devices and cabin air pressuretransducers placed in various locations within the aircraft.

In an eighth embodiment of the invention illustrated in FIG. 10,multiple simple inlet valves are placed at various locations within theoxygen distribution piping system, with a pressure transducer downstreamof each inlet valve. In this embodiment, the emergency oxygen supplysystem 150 includes a source of supplemental breathable oxygen 152, suchas one or more cylinders of compressed oxygen, for example, which servesto store a required supply of oxygen. A conduit 154 is connected to thesource of supplemental breathable oxygen to provide a flow of oxygen,controlled by a first relatively simple upstream on-off inlet valve V₁(156), and a second relatively simple downstream on-off inlet valve V₂(158), such as a two-position solenoid valve, for example, connectedserially to a set 159 of breathing devices 160 a, 160 b, 160 c,typically including one or more individual reservoir bags and attachedface masks. A single pressure controller 162 is connected to the inletvalves and controls the operation of the inlet valves via control lines163 a, 163 b in response to input signals received from a first pressuretransducer P_(A) (164), representing the cabin pressure and acorresponding altitude, input signals received from a second pressuretransducer P₁ (166 a), downstream from the upstream on-off valve V₁, anda third pressure transducer P₂ (168 a), downstream from the downstreamon-off valve V₂, representing the current gas pressure downstream of themonitored valves. Each valve and associated pressure transducer set isconnected to the controller by a separate set of wires. The controllermay have multiple independent channels, so that each valve andassociated pressure transducer has a dedicated control channel.Alternatively, the controller could be sequenced so that the signal fromone downstream pressure transducer at a time is read, and its associatedvalve is pulsed if the pressure value detected is low enough to requirethis action.

In this embodiment, oxygen delivery pressure can be set to an optimumvalue zone by zone, without performance being limited by the differencesin flow rates at various locations in the piping network that resultfrom variations in pressure drops within different regions of the pipingnetwork. This configuration also allows for a zoned-system architecture,with one or more pressure controllers and their corresponding sources ofsupplemental breathable oxygen, inlet valves, breathing devices andcabin air pressure transducers placed in various locations within theaircraft.

In a ninth embodiment of the invention, illustrated in FIG. 11, anemergency oxygen supply system 170 includes a source of supplementalbreathable oxygen 172, such as one or more oxygen cylinders. In thelimiting case of such an approach, each cabin occupant may be served bya separate one-person cylinder. A conduit 174 is connected to the sourceof supplemental breathable oxygen to provide a flow of oxygen,controlled by a relatively simple on-off inlet valve 176, such as atwo-position solenoid valve, for example, to an individual breathingdevice 178, typically including a reservoir bag and an attached facemask. Such one-person, small oxygen cylinders and associated apparatusfor the emergency oxygen supply system can be distributed throughout thepassenger cabin area of an airplane. Each oxygen vessel is fitted with asimple pressure reducing regulator 180, with no altitude-compensatingfeatures included. Downstream of the inlet valve, a manifold 182 isinterposed between the inlet valve and its associated reservoir bag.

A single pressure controller 184 is connected to and controls theoperation of the inlet valve via a control line 186 in response to afirst input signal received from a single pressure transducer P_(A)(188), representing the cabin pressure and a corresponding altitude. Thecontroller evaluates the pressure transducer signal and generates asingle signal to the simple inlet valve. In this case, there is anintrinsic flow rate that would be achieved through each dispensingorifice if the simple inlet valve were to be continuously open. Thisintrinsic flow rate is a function of the output pressure from thepressure reducer and the properties of the dispensing orifices.Depending on the flow that is appropriate for the given altitude, thevalve-operating signal is applied for a suitable fraction of theoperating time. The flow rate achieved by the dispensing orifice is thenequal to the intrinsic flow rate possible multiplied by the fraction oftime the inlet valve is open. For example, if the intrinsic flow ratepossible when the inlet valve is open continuously is 4 liters perminute and the valve is open 30% of the time, the flow rate achieved is1.2 liters per minute. This configuration also allows for a zoned-systemarchitecture, with one or more pressure controllers and theircorresponding sources of supplemental breathable oxygen, inlet valves,breathing devices and cabin air pressure transducers placed in variouslocations within the aircraft.

As is illustrated in FIG. 12, in a variation of the ninth embodiment, inwhich the same elements from FIG. 11 are indicated by the same referencenumbers as in FIG. 11, more than one cabin occupant may be served byeach source of supplemental oxygen 172 of the emergency oxygen supplysystem 170. A conduit 174 is connected to the source of supplementalbreathable oxygen to provide a flow of oxygen, controlled by arelatively simple on-off inlet valve 176, such as a two-positionsolenoid valve, for example, to a set 178 of breathing devices 179 a,179 b, 179 c, 179 d, each typically including one or more individualreservoir bags and attached face masks. Each oxygen vessel is fittedwith a simple pressure reducing regulator 180 with noaltitude-compensating features included. Downstream of the inlet valve,a manifold 182, fitted with one or more dispensing orifices, isinterposed between the inlet valve and its associated reservoir bag.Each manifold orifice typically supplies more than one oxygen mask. Asingle pressure controller 184 is connected to and controls theoperation of the inlet valve via a control line 186 in response to afirst input signal received from a single pressure transducer P_(A)(188), representing the cabin pressure and a corresponding altitude.This configuration also allows for a zoned-system architecture, with oneor more pressure controllers and their corresponding sources ofsupplemental breathable oxygen, inlet valves, breathing devices andcabin air pressure transducers placed in various locations within theaircraft.

In a tenth embodiment of the invention, illustrated in FIG. 13, anemergency oxygen supply system 190 includes a source of supplementalbreathable oxygen 192, such as a relatively small oxygen cylinder. Suchone-person, small oxygen cylinders and associated apparatus for theemergency oxygen supply system can be distributed throughout thepassenger cabin area of an airplane. As is shown in FIG. 13, each cabinoccupant may be served by a separate one-person cylinder, although morethan one person may be served by each oxygen supply cylinder, as isfurther described below. A conduit 194 is connected to the source ofsupplemental breathable oxygen to provide a flow of oxygen, controlledby a relatively simple on-off inlet valve 196, such as a two-positionsolenoid valve, for example, to an individual breathing device 198,typically including a reservoir bag and an attached face mask. In thisembodiment, a pressure reducer at the outlet of the local oxygen vesselis eliminated. Downstream of the inlet valve, a manifold 197 isinterposed between the inlet valve and its associated reservoir bag.

A single pressure controller 200 is connected to the inlet valve andcontrols the operation of the inlet valve via a control line 202 inresponse to an input signal received from a single pressure transducerP_(A) (204), representing the cabin pressure and a correspondingaltitude. The controller evaluates the pressure transducer signal andgenerates a signal to the simple inlet valve. In this case, there is anintrinsic flow rate that would be achieved through each dispensingorifice if the simple inlet valves were continuously open. Thisintrinsic flow rate is a function of the output pressure from thepressure reducer and the properties of the dispensing orifices.Depending on the flow that is appropriate for the given altitude, thevalve-operating signal is applied for a suitable fraction of theoperating time. The flow rate achieved by each dispensing orifice isthen equal to the intrinsic flow rate possible multiplied by thefraction of time the inlet valve is open. For example, if the intrinsicflow rate possible when the inlet valve is open continuously is 4 litersper minute and the inlet valve is open 30% of the time, the flow rateachieved is 1.2 liters per minute. This configuration also allows for azoned-system architecture, with one or more pressure controllers andtheir corresponding sources of supplemental breathable oxygen, inletvalves, breathing devices and cabin air pressure transducers placed invarious locations within the aircraft.

As is illustrated in FIG. 14, in a variation of the tenth embodiment, inwhich the same elements from FIG. 13 are indicated by the same referencenumbers as in FIG. 13, more than one cabin occupant may be served byeach source of supplemental breathing oxygen 192 of the emergency oxygensupply system 190. A conduit 194 is connected to the source ofsupplemental breathable oxygen to provide a flow of oxygen, controlledby a relatively simple electrical on-off inlet valve 196, such as atwo-position solenoid valve, for example, to a corresponding set 198 ofbreathing devices 199 a, 199 b, 199 c, 199 d, typically including one ormore individual reservoir bags and attached face masks, respectively.Downstream of the inlet valve, a manifold 197, fitted with one or moredispensing orifices, is interposed between the inlet valve and itsassociated reservoir bag. A single pressure controller 200 is connectedto the inlet valve and controls the operation of the inlet valve via anetwork of control lines 202 in response to a first input signalreceived from a single pressure transducer P_(A) (204) representing thecabin pressure and a corresponding altitude. An intrinsic flow rate canbe achieved at any given point in time through each dispensing orificewhen the simple inlet valve is open continuously. However, this flowrate changes as the pressure in the oxygen storage vessel upstream ofthe dispensing orifice decays with the passage of time during operationof the equipment. The flow rate is a function of the operating timehistory and the pressure decay properties of the oxygen storage unit, aswell as the properties of the dispensing orifices themselves. In thiscontext, the “operating time” refers to the time the valve remains open,which is not necessarily equal to the total elapsed time since thebeginning of a decompression incident causing supplemental oxygen to beused. This configuration also allows for a zoned-system architecture,with one or more pressure controllers and their corresponding sources ofsupplemental breathable oxygen, inlet valves, breathing devices andcabin air pressure transducers placed in various locations within theaircraft.

The single pressure transducer senses the cabin pressure altitude. Thecontroller contains information that mathematically describes the way inwhich the pressure in the oxygen storage vessel decays as a function ofoperating time. The controller also measures and retains informationabout the operating time history during the period of use. Thecontroller evaluates the pressure transducer signal and the operatingtime history and generates a single signal to the simple inlet valve.Depending on the flow that is appropriate for the combination of givenaltitude and given previous operating time history, the valve-operatingsignal is applied for a suitable fraction of the operating time. Theflow rate achieved by each dispensing orifice is then equal to theintrinsic flow rate possible multiplied by the fraction of time thevalve is open.

As an illustrative example, assume that the cabin pressure altitude issuch that it is desired to deliver a flow rate of 2 liters per minute.Initially, the combination of contained pressure within the cylinder andthe orifice characteristics would allow a flow of 5 liters per minute ifthe valve were open continuously. Because appropriate data are stored inthe controller, the controller initially opens the valve 40% of thetime, resulting in an appropriate 2 liter per minute flow rate. Aftersome period of operating time has elapsed, the contents within thecylinder are partially discharged, lowering the contained pressure to anextent that a flow of 3 liters per minute would be possible if the valvewere continuously open. By tracking the history of how long the valvehas been open and using this stored information in combination withother stored information about the properties of the equipment, thecontroller can calculate that this condition prevails. The controllerthen opens the valve 67% of the time to continue delivering a flow rateof 2 liters per minute.

In many gaseous oxygen systems, at the start of operation a surge ofoxygen is delivered for a few seconds to provide sufficient pressure tooperate pneumatic latches that release the doors of the compartmentswhere the oxygen masks are stowed prior to need. It will be apparentthat within the teachings of this invention such a surge could beprovided by the controller if desired.

Another way of opening the doors of the compartments is by an electricallatch. Usually, power for the latch circuit would be suppliedindependently of the power supplied to the electrical valves used in myinvention. However, the electrical latches could be wired into the samecircuit as these valves. In that case, the latches would draw power eachtime the valve was powered. This added power consumption might be anacceptable trade-off for elimination of the weight associated with thewires of a second power circuit for the latches.

A latch may also be equipped with a feature such that energizing thelatch to release the doors also performs an action that opens a contactwithin the latch, interrupting continuity through the latch so that thelatch cannot draw power again until a contact position is reset. In thiscase, the latch draws power needed to release the door only the firsttime the circuit is energized, but the door latch does not draw powerwhen subsequent power pulses are applied to the circuit. A suitableseries-parallel circuit would permit the valve to continue to operatewithout continuity through the latch.

In many oxygen systems, some redundant components are sometimesinstalled to enhance the overall system reliability. This practice couldbe followed within the scope of my invention. For example, although theembodiments as described above have mentioned the use of a singlepressure transducer to sense cabin altitude pressure, adding a secondredundant transducer would lie within the intended scope of myinvention. Similarly, the use of wiring arrangements that provideredundant connections to protect against possible deactivation of theequipment due to damage to the wiring would lie within the intendedscope of my invention.

It will be apparent from the foregoing that, while particular forms ofthe invention have been illustrated and described, various modificationscan be made without departing from the spirit and scope of theinvention. Accordingly, it is not intended that the invention belimited, except as by the appended claims.

The invention claimed is:
 1. An emergency oxygen supply system for anaircraft with a pressurizable passenger cabin comprising: a source ofsupplemental breathable oxygen; a conduit connected to said source ofsupplemental breathable oxygen; an upstream first on-off inlet valveconnected to said conduit downstream from said source of supplementalbreathable oxygen; a downstream second on-off inlet valve connected tosaid conduit downstream serially from said first on-off inlet valve; aplurality of breathing devices connected to said conduit downstream fromsaid downstream second on-off inlet valve; at least one cabin airpressure transducer for generating a cabin air pressure input signalrepresenting the cabin pressure and a corresponding altitude; a secondpressure transducer connected to said conduit between said upstreamfirst on-off inlet valve and said downstream second on-off inlet valve,and a third pressure transducer connected to said conduit between saidsecond on-off inlet valve and said plurality of breathing devices, saidsecond and third pressure transducers being configured to sense a gaspressure in said conduit at locations downstream of the first and secondon-off inlet valves, respectively; and a pressure controller connectedto said at least one cabin air pressure transducer for receiving saidcabin air pressure input signal, said pressure controller beingconnected to and controlling the operation of said first and secondon-off inlet valves in response to said cabin air pressure input signalreceived from said at least one cabin air pressure transducer, and saidpressure controller being operative to control the operation of saidfirst and second on-off inlet valves in response to said second andthird pressure transducers, respectively.
 2. The emergency oxygen supplysystem of claim 1, wherein said inlet valve comprises a two-positionsolenoid valve.
 3. An emergency oxygen supply system for an aircraftwith a pressurizable passenger cabin comprising: a plurality of sourcesof supplemental breathable oxygen; a corresponding plurality of conduitsconnected to said plurality of sources of supplemental breathableoxygen, respectively; a corresponding plurality of upstream first on-offinlet valves connected to said corresponding plurality of conduits,respectively, and a corresponding plurality of downstream second on-offinlet valves, connected to said corresponding plurality of conduitsdownstream serially from said plurality of first on-off inlet valves,respectively; a corresponding plurality of sets of pluralities ofbreathing devices connected to said corresponding plurality of conduitsdownstream from said plurality of downstream second on-off inlet valves,respectively; at least one cabin air pressure transducer for generatinga cabin air pressure input signal representing the cabin pressure and acorresponding altitude; a plurality of second pressure transducersconnected to said corresponding plurality of conduits between saidplurality of upstream first on-off inlet valves and said plurality ofdownstream second on-off inlet valves, respectively, and a plurality ofthird pressure transducers connected to said corresponding plurality ofconduits between said plurality of downstream second on-off inlet valvesand said corresponding plurality of sets of pluralities of breathingdevices, respectively, said plurality of second pressure transducersbeing configured to sense a gas pressure in said corresponding pluralityof conduits between said plurality of upstream first on-off inlet valvesand said plurality of downstream second on-off inlet valves,respectively, and said plurality of third pressure transducers beingconfigured to sense a gas pressure in said corresponding plurality ofconduits between said plurality of second on-off inlet valves and saidcorresponding plurality of sets of pluralities of breathing devices,respectively; and a pressure controller connected to said at least onecabin air pressure transducer for receiving said cabin air pressureinput signal, said pressure controller being connected to andcontrolling the operation of said plurality of upstream first on-offinlet valves and said plurality of downstream second on-off inlet valvesin response to said cabin air pressure input signal received from saidat least one cabin air pressure transducer, and said pressure controllerbeing operative to control the operation of said plurality of upstreamfirst on-off inlet valves and said plurality of downstream second on-offinlet valves in response to said second and third pressure transducers,respectively.